Two national civil rights groups have joined a federal lawsuit accusing dozens of Oklahoma sheriffs, judges and court clerks of operating a debt-collection scheme that preys on poor people by sending them to jail if they can't pay court costs.

U.S. Attorney General Jeff Sessions told dozens of Oklahoma sheriffs on Thursday that policymakers should exercise caution when considering easing tough sentencing laws, a hot political topic in a state with one of the highest incarceration rates in the country.

Friction between the state’s new prisons director and some county sheriffs over how quickly the Department of Corrections is picking up inmates from county jails is flaring up again this session over a pair of bills moving through the Legislature.